I'm not sure I can think of 10, here's some of the most obvious ones from both my experience and reading others:
- Bad leadership. Often born from the leader of the guild being somebody who thinks they should be a leader (ie. self important) but lacks any of the skills to do so, such as being able to deal with people, organizing all of the necessity of a guild or possessing a high level of knowledge of the game.
- Bad management. Partially linked to the above, a lot of guild can have poor officers/leadership that fails to give the guild direction. A lot of the important positions in the guild are given to people who are the closest friends of the leadership but don't possess the necessary skills to do their job (like class leaders who aren't that good at their class). I made it a separate reason to the above because a guild can always have a fairly decent leader but a couple of judgment errors in terms of creating his/her support team could result in a rift between either them and their officers or their guildies. The opposite is also true, but generally in these cases the leader is ditched and a new guild is formed with relative ease.
- Poor recruitment pool. This could either be a low pop server or just a general shortage of skilled player in a certain class. In TBC a good example alliance side was getting enough good resto shamans. Although class balance isn't as tight anymore, a guild could have problems if they're stuck in a perpetual state of healer shortage, for example.
- Summer. Although the majority of players can commit to a schedule over summer, there can often be a significantly damaging amount of player who won't bother over summer. This is a more crucial issue when the guild isn't doing so well and these players take the chance to jump the boat or dodge wipe nights for several months. The shortage cannot be covered by recruitment either because everyone else is in a similar boat.
- Poor players. Both presently and new recruits. A guild can go through many trials and they could all be terrible. This in turn can produce a knock on effect of demoralizing the better players and some may stop playing/ leave which again means gaps are plugged by poor players or not at all. A large portion of poor players already in guild can dissuade new recruits that are joining your guild, preventing you from increasing you good player - bad player ratio and be stuck in a never ending cycle.
- Crap stirrers. Related to poor players but a crap stirrer won't always be a crap player. Generally if you have one or two people in a guild who get uppity about things or occasionally have arguments with other players it's not much of a problem, but if you get 4 or 5 regularly in a raid you're bound to get people getting rubbed the wrong way constantly. This will cause people to leave and likewise, will cause new recruits to leave during a trial.
- Cliques. This often happens when the remnants of two guild merge for better or worse. A lot of cliques can be generally harmless but if friction develops somehow, usually early on, by an argument between two members of separate cliques or an obvious completly opposing opinion on how things should be go between the two then a guild can quickly divide.
- Bad Rules. Partially related to leadership but won't always be just attributed to the leader. If a looting method and other rules that are set up in a guild are not fair or encouraging then players can get disheartened. Likewise certain rules can be a big catalyst for regular arguments, which in turn break down the morale of the guild.
- Lack of challenge. Quite often before an expansion people may take a sabbatical because there isn't much left to do, particularly if a guild has all content cleared. This could cause inactivity that prevents raiding and therefore the raider who are left may leave and condemn the guild. Similarly, if a large part of the guild's goal is to do hard modes but there's never the time or the skilled/geared players to allow it to do so, these players may tire of farming normals after a while and seek out challenges elsewhere.
- Unforeseen circumstances. Your MTs could be sick for long periods or there could be real life issues preventing even your leader(s) from being around. A guild that is unable to continue without a few players can be crippled by their absence.
Spelling corrected because I'm OCD like that sometimes- Pen
- good job, cause I make plenty of typos when hammering out a wall of text and cba to correct - X